The present invention relates to a structure of a magnetic circuit in a linear pulse motor.
The linear pulse motor stepwisely propels and positions a forcer, which may be either a scale or a magnetic flux generating unit, in accordance with pulse signals supplied to the unit. A typical example of the permanent magnet-type linear pulse motor is diagrammatically illustrated in FIG. 1, in which reference numeral 1 designates an elongated plate scale as a stator in the upper face of which are longitudinally formed a row of teeth 1a, 1a, . . . with a predetermined pitch. Above the scale 1 there is disposed a magnetic flux generating unit 7 as a forcer to be movable along the scale 1 by a suitable supporting means (not shown), the unit including a permanent magnet 6 and a pair of U-shaped cores 4 and 5 each having a coil 2 or 3 wound around them and magnetically interconnected through the magnet 6 in a serial manner with polarity of the magnet 6 as shown in FIG. 1. Magnetic poles 4a and 4b of the core 4 and magnetic poles 5a and 5b of the core 5 are shifted 1/2 of the pitch of the teeth 1a of the scale 1 with respect to the teeth and the cores 4 and 5 are disposed with a shift of 1/4 of the pitch.
The magnetic circuit of this prior art linear pulse motor has a structure such that both the magnetic flux of generated by the coils 2 and 3 and the magnetic flux of the permanent magnet 6 longitudinally pass through the scale 1 and hence the permanent magnet 6 and cores 4 and 5 must be serially arranged along the direction of travel of the forcer 7. Thus this motor is disadvantageous in that the forcer is long in the direction of the travel thereof.
A flat-type linear pulse motor was proposed in U.S. patent application Ser. No. 543,927 (filed: Oct. 20, 1983), now U.S. Pat. No. 4,578,622 corresponding to Japanese Patent Application No. 57-198,658, of which disclosure is hereby incorporated by reference. One embodiment disclosed in this patent application is illustrated in FIG. 2, in which 10 and 11 are U-shaped core units having coils 12 and 13 wounded around them, respectively. These core units 10 and 11 are horizontally disposed so that magnetic poles 10a and 10b and magnetic poles 11a and 11b are opposed to each other, respectively, and the core units are bonded through adhesive to a permanent magnet 16. In the upper surface of each of the poles 10a, 10b, 11a and 11b, a comb-shaped tooth portion 10a', 10b', lla'or 11b'is formed. An attaching plate 17 is bonded to the lower face of the permanent magnet 16. The forcer 18 thus constructed has a guide passage defined by guide members 14 and 15 and the magnetic poles 10a, 10b, 11a and 11b and a plurality of balls 19, 19, . . . are rotatably retained the lateral peripheries of the guide passage. The scale 1 is placed above the magnetic poles 10a, 10b, 11a and 11b by resting the lateral peripheries of the scale 1 on the balls 19, so that the scale 1 is longitudinally propelled and positioned by supplying a predetermined number of pulse signals to the coils 12 and 13. This liner pulse motor considerably satisfies requirement in reduction in volume, but it is disadvantageous in that the magnetic flux generating unit 18 is long in the longitudinal direction of the scale 1 and in that the magnetic path through which magnetic flux generated from the coils 12 and 13 is long and wide, so that flux leakage is large, resulting in relatively large power consumption.